Southwest Michigan field crops update – August 27, 2026

Nicolle Ritchie<ritchi67@msu.edu> and Angie Gradiz<gradizme@msu.edu>, Michigan State University Extension - August 27, 2026

Watch for red crown rot in soybeans. Tar spot was confirmed in St. Joseph and Van Buren counties. No further late blight has been detected in southwest Michigan.

Photo by Nicolle Ritchie, MSU Extension.

Weather

Except for a couple of light pop-up showers, the past week was dry and warm with cool nights. Temperatures will increase a little for the upcoming week, although precipitation is expected to remain low. With potato harvest ongoing and seed corn harvest set to start soon, dry weather is good news.

WU 10-day as of 8-27.png — Ten-day Weather Underground forecast for Kalamazoo as of August 20.

6-10 and 8-14 as of 8-27.png — The 6-10 day (Sept. 1-5, top) and 8-14 day (Sept. 3-9, bottom) outlooks for temperature (left) and precipitation (right).

Crops and pests

Full-season soybeans are finishing R5 (seed fill) and entering R6 (full seed). Continue to watch out for red crown rot, which is a disease not yet confirmed in Michigan that looks similar to sudden death syndrome and brown stem rot. If you suspect red crown rot, submit a sample to the Michigan State University Plant and Pest Diagnostics Lab. Michigan Soybean Committee and the United Soybean Board will cover the diagnostic fees. You can also request a soybean sampling kit.

26 soybeans R6 2.jpeg — Soybeans at R6, at which point seeds have filled the whole cavity. The pod will begin to change color and dry down as it moves toward R7. Photo by Nicolle Ritchie, MSU Extension.

25 SDS early.jpg — Earlier foliar symptoms of sudden death syndrome (SDS), which look similar to foliar symptoms of red crown rot. Photo by Nicolle Ritchie, MSU Extension.

Corn kernel development continued, with fields mostly ranging from R4 (dough) to R5 (dent). Seed corn continues to dry down, and harvest will begin soon. Tar spot was confirmed in St. Joseph and Van Buren counties this week. Unless the tar spot pressure is considerable, there is little benefit to going after tar spot with a fungicide at this point in the season.

26 tar spot see lesions.png — Early tar spot lesions (circled). The lesion is a matte black, slightly raised, that does not wipe off or dissolve with water. Photo by Nicolle Ritchie, MSU Extension.

The Crop Protection Network’s Tar Spot Map showing Michigan counties with confirmed tar spot as of August 27. Counties in gold have had tar spot confirmed in 2026.

Late blight was found in St. Joseph County potatoes two weeks ago, and there have been no further detections. Last week, the farm with the late blight detection generously hosted an in-person identification and management meeting, organized by crop consulting company Mid-Michigan Agronomy, who detected and genotyped the late blight.

While late blight’s sporulation pattern can be diagnostic, the sporulation is only visible under certain environmental conditions. Other diagnostic clues for late blight identification include black (not brown or gray) lesions that can spread across veins and curling or twisting inward of the lesion. For more photos and information on the late blight risk over the past week, check out the article “Current status of potato late blight in Michigan—August 18, 2026”. To reduce late blight spread, use bleach to decontaminate footwear and clothing between fields.

26 late blight lesion curl twist.jpeg — Old late blight lesion. This lesion is black, curls or twists inward and is not contained by leaf veins. Photo by Nicolle Ritchie, MSU Extension.

Irrigation and water use

Corn and soybeans remain at peak water use, requiring approximately 1.2 inches of water per week (0.17 inches per day). Maintaining adequate soil moisture during these critical growth stages is important to minimize water stress and protect yield potential. To identify water stress, look for rolled or curled leaves in corn and grayish or turned leaves in soybeans during the evening.

Potato water use continues to decline as the crop approaches maturity. Potatoes in the tuber bulking stage require approximately 0.70 inches of water per week, while potatoes in the pre-senescence stage require approximately 0.35 inches per week. Irrigation should be adjusted as the crop matures and water demand decreases.

Rainfall this week is expected to be limited, with higher temperatures increasing evapotranspiration and crop water demand. When irrigating soybeans, using higher application rates can reduce the frequency of leaf-wetting events, which may help reduce conditions favorable for white mold development.

To improve irrigation management, consider using irrigation scheduling tools such as the free and updated MSU Irrigation Scheduling Mobile App, available for Apple and Android devices. The app provides field-specific irrigation recommendations based on crop growth, weather, and soil type.

This year, weekly crop water use updates will continue to be shared through the Southwest Michigan Crop Updates, and for added convenience, updates will also be sent through direct email and text messages. If you would like to see an additional location included in the report, please contact Angie Gradiz at gradizme@msu.edu or 531-249-4956.

The table below summarizes estimated crop water use (inches per week) for major irrigated field crops across Michigan's primary irrigated regions.

Estimated weekly crop water use for field crops in Michigan (in/week) for the week of Aug. 24-30, 2026:

Crop	Growth stage	Constantine	Berrien Springs	Entrican	Hart
	Reference ET	1.11	1.19	1.07	1.08
Corn	V14	1.22	1.31	1.18	1.19
Corn	VT, Silk, Blister, Dough, Begin Dent	1.22	1.31	1.18	1.19
Corn	Full Dent	1.11	1.19	1.07	1.08
Soybeans	R2 (Full bloom)	1.22	1.31	1.18	1.19
Soybeans	R3 (Begin pod) - R4 (Full pod)	1.22	1.31	1.18	1.19
Soybeans	R5 (Begin seed) - R6 (Full seed)	1.22	1.31	1.18	1.19
Potatoes	Bulk	0.67	0.71	0.64	0.65
Potatoes	Pre-Senescence	0.33	0.36	0.32	0.32
Potatoes	Maturity	0.11	0.12	0.11	0.11

Field Crops Virtual Breakfast Series

General Virtual Breakfast promo pic.png

Irrigation investment economics, presented by Lyndon Kelley, was the topic for the MSU Extension Field Crops Virtual Breakfast this week. Irrigation comes with advantages and disadvantages—the ability to improve yield can increase income, but irrigation installation, repair and maintenance are costly. Before investing in irrigation, weigh the costs and benefits.

Recordings of this and all the Virtual Breakfast meetings are closed-captioned and available at the Field Crops Virtual Breakfast webpage and the MSU Extension Field Crops Team social media platforms: Facebook, Spotify, Mediaspace, YouTube, Apple Podcasts and Twitter/X.

This work is supported by the Crop Protection and Pest Management Program (grant no 2024-70006-43569) from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).